Vacuum treatment of coated direct-positive silver halide elements

ABSTRACT

THIS INVENTION RELATES TO PROCESSES FOR IMPROVING THE PHOTOGRAPHIC PROPERTIES OF FOGGED, DIRECT-POSITIVE, SILVER HALIDE EMULSIONS. IN ONE ASPECT, COATED, DIRECT-POSITIVE EMULSIONS ARE SUBJECTED TO A VACUUM TRATMENT WHEREBY THE MAXIMUM DENSITY STABILITY IS IMPROVED UPON AGING. THE DMAX STABILITY IS HIGHLY IMPROVED IN PREFERRED EMBODIMENTS WHEN ELECTRON-ACCEPTOR COMPOUNDS OR DESENSITIZERS ARE PRESENT IN THE EMULSION.

United States Patent VACUUM TREATMENT OF COATED, DIRECT- POSITIVE,SILVER HALIDE ELEMENTS Richard Karl Kurz, Rochester, N.Y., assignor toEastman Kodak Company, Rochester, N.Y. No Drawing. Filed Mar. 25, 1970,Ser. No. 22,697 Int. Cl. G03c 5/24 US. C]. 96-64 6 Claims ABSTRACT OFTHE DISCLOSURE Ihis invention relates to processes for improving thephotographic properties of fogged, direct-positive, silver halideemulsions. In one aspect, coated, direct-positive emulsions aresubjected to a vacuum treatment whereby the maximum density stability isimproved upon aging. The D stability is highly improved in preferredembodiments when electron-acceptor compounds or desensitizers arepresent in the emulsion.

This invention relates to improved silver halide emulsions and methodsof treating coated, direct-positive, silver halide emulsions to improvethe photographic properties thereof. In one aspect, this inventionrelates to a process of subjecting coated silver halide emulsions orsilver halide emulsion layers to a vacuum to stabilize the photographicproperties; in one instance, the maximum density of fogged silver halideemulsions is stabilized upon aging, especially in fogged direct-positiveemulsions containing densitizer compounds or electron acceptors.

It is known in the art to use various chemical addenda to stabilize theproperties of silver halide emulsions upon aging. In certain instances,halide ions have been used to stabilize photographic properties such assensitivity of silver halide emulsions. In other instances, it hasbecome necessary to control temperature, humidity and the like carefullyduring shipping and storage to minimize the loss of image density andthe increases in background fog. In some instances, formaldehyde hasbeen added to the coated silver halide emulsions to improve agingproperties or, in still other systems, the coated emulsions have beendesiccated to improve properties, However, it is desirable to provideimproved simple techniques for stabilizing the photographic propertiesof silver halide emulsions, especially fogged, direct-positive, silverhalide emulsions which are not as easily stabilized as negativeemulsions.

I have now found that the stability of fogged, directpositive silverhalide emulsions can be improved when the coated emulsions or emulsionlayers are subjected to a vacuum of at least 1 torr and preferably of atleast 0.1 torr. The coated layer is subjected to the vacuum for a periodof at least 1 minute and preferably at least 5 minutes. Very goodimprovements in stability of the emulsion are obtained by thisprocedure, especially with fogged, direct-positive, silver halideemulsions containing electron acceptors.

While it is known that vacuum treatment of negative emulsions containingcertain compounds will reduce desensitization of the emulsion, i.e.,loss of photographic speed, or that in other instances it will increasespeed of negative emulsions, it is quite unexpected that the maximumdensity stability of fogged, direct-positive emulsions would be affectedby vacuum treatment of the emulsion as discovered in this invention.

In one preferred embodiment, the silver halide emulsions treated inaccordance with this invention contain an electron-accepting compoundwhich has an anodic polarographic halfwave potential and a cathodichalfwave potential which, when added together, give a positive sum.

ice

In another preferred embodiment of this invention, the fogged,directpositive emulsions treated in accordance with this inventon arereduction and gold fogged.

In another embodiment of this invention, the fogged silver halideelements which comprise at least one layer of a fogged, direct-positiveemulsion are subjected to an effective vacuum at the surface of saidelement of at least 1 torr and preferably at least 0.1 torr for at least1 minute and preferably at least 5 minutes.

The direct-positive silver halide compositions which can be improved bythe present process can be generally classified asblue-sensitive-direct-positive silver halide compositions. It isunderstood that blue-sensitive means that the direct-positivecompositions will provide a reversal image when exposed with light inthe 350- to 500 millimicron range of the electromagnetic spectrum andthen developed. The silver halide compositions can also be spectrallysensitized so as to form reversal images when exposed in other regionsof the spectrum such as in the green and red regions. However, they allhave the property of being capable of forming a reversal image whenexposed with light in the blue region of the visible spectrum.

Typical direct-positive silver halide compositions which can be treatedin accordance with the present invention include:

(1) Emulsions containing fogged silver halide grains which have internalcenters for the deposition of photolytic silver such as those generallydisclosed in Berriman, 15. Pat. 3,367,778 issued Feb. 6, 1968, includingemul- SlOIlS comprising grains which have centers which promote thedepositon of silver which are either sufficiently small or sufficientlyburied within the crystal as to be not accessible to initiate surfacedevelopment to a visible image. Silver halide grains of this latter typecan be provided by (a) using a very low concentrations of sensit1z1n gagent throughout the precipitation, (b) adding the sensitizing agent tothe precipitation medium during the initial part of the precipitationand (c) reducing part of the silver nitrate used in the initial portionof the prec1p1tat1on, etc.

2) Emulsions which contain silver halide grains WhlCh are uniformlyfogged to specific levels and contain electron-accepting compoundsadjacent the grains, as described in Illingsworth, U.S. Ser. No. 619,948filed Mar. 2, 1967, now Pat. No. 3,501,305.

(3) Emulsions comprising fogged regular grains which contain anelectron-accepting compound of desensitizer adjacent the grains, asdescribed in Illingsworth, U.S. Ser. No. 619,909 filed Mar. 2, 1967, nowPat, No. 3,501,306.

(4) Emulsions comprising monodispersed grains which have been reductionand gold fogged, as described in Illingsworth, U.S. Ser. No. 619,936filed Mar. 2, 1967, now Pat. No. 3,501,307.

(5) Emulsions similar to the above which provide a reversal image whenexposed to blue light.

The silver halides employed in the preparation of the photographiccompositions described herein include any of the photographic silverhalides as exemplified by silver bromide, silver chloride, silverchlorobromide, silver bromoiodide, silver chlorobromide, and the like.Silver halide grains having a mean grain diameter, i.e., an averagegrain size in the range of about .01 to about 2 microns, preferablyabout .02 to about 1 micron, give particularly good results in reversalsystems. The silver halide grains can be any suitable shape such ascubic or octahedral, but they are preferably cubic, and more preferablycubic-regular. The preferred photographic silver halide emulsionscomprise at least 50 mole percent bromide, the most preferred emulsionsbeing silver bromoiodide emulsions, particularly those containing lessthan about 10 mole percent iodide. 'Ihe photographic silver halides canbe coated at silver coverages in the range of about 50 to about 500milligrams of silver per square foot of support.

The direct-positive photographic silver halide emulsions of thisinvention contain silver halide grains which are fogged. Fogging can beelfected by chemically or physically treating the photographic silverhalides by methods previously described in the prior art. Such foggingcan be accomplished by various techniques such as chemical sensitizationto fog, particularly good results being obtained with techniques of thetype described by Antoine Hautot and Henri Saubenier in Science etIndustries Photographiques, vol. XXVIII, January 1957, pages 57-65. Thesilver halide grains can 'be fogged with the high-intensity light,reduction fogged with a reducing agent such as thiourea dioxide orstannous chlorideor fogged with gold or noble metal compounds.Combinations of reduction fogging agents with gold compounds orcompounds of another metal more electropositive than silver, e.g.,rhodium, platinum or iridium, can be used in fogging the silver halidegrains. The fogged silver halide grains in the direct-positivephotographic emulsions of this invention give a density of at least 0.5when developed without exposure for minutes at 68 F. in Kodak DK- 50developer when a direct-positive emulsion containing such grains iscoated at a coverage of 50 to about 500 mg, of silver per square foot ofsupport.

The direct-positive photographic emulsions of this invention preferablycomprise reduction and gold fogged silver halide grains, i.e., silverhalide grains which are fogged with a combination of a reduction foggingagent and a gold fogging agent. Generally, about 0.0005 to about 0.06,preferably about 0.001 to about 0.03, milliequivalent of reductionfogging agent per mole of silver halide is employed in fogging thesilver halide grains in certain embodiments of this invention. Examplesof suitable reduction fogging agents which can be employed in thepractice of this invention include hydrazine, phosphonium salts such astetra(hydroxy methyl)phosphonium chloride, t-hiourea dioxide asdisclosed in 0.8. Pats. 3,062,651 by Hillson issued Nov. 6, 1962, and2,983,609 by Allen et a1. issued May 9, 1961, reducing agents such asthe stannous salts, e.g., stannous chloride, as disclosed in US. Pat.2,487,850 by Carroll issued Nov. 15, 1939, polyamines such as diethylenetriamine as disclosed in US. Pat. 2,519,698 by Lowe 'et al. issued Aug.15, 1950, polyamines such as spermine as disclosed in US. Pat. 2,521,925by Lowe et a1. issued Sept. 12, 1950, bisQS-aminoethyl) sulfide and itswater-soluble salts as disclosed in U.S. Pat. 2,521,926 by Lowe et al.issued Sept. 12, 1950, and the like.

The gold fogging agents which can be employed in practicing thisinvention can be any gold salt suitable for use in fogging photographicsilver halide grains and includes the gold salts disclosed in US. Pats.2,399,083 by Waller et al. issued Apr. 23, 1946, and 2,642,361 byDamschroder et al. issued June 16, 1953. Specific examples of goldfogging agents are potassium chloroaurite, potassium aurithiocyanate,potassium chloroaurate, auric triohloride, Z-aurosulfobenzothiazolemetho chloride, and the like. The concentration of gold foggi g agentemployed in the practice of this invention is subject to variation, butis generally in the range of about 0.001 to about 0.01 millimole permole of silver halide. Potassium chloroaurate is a preferred goldfogging agent and is often used at concentrations of less than about 5mg. per mole of silver halide and preferably at concentrations in therange of about 0.5 to about 4 mg. per mole of silver halide.

Preferably, the direct-positive emulsions used in this invention containelectron-accepting compounds, often referred to as desensitizers orelectron traps, which are generally compounds having an anodicpolarographic halfwave potential and a cathodic polarographic potentialwhich, when added together, give a positive sum. Typical usefulelectron-accepting compounds, along with methods of determining thepolarographic potentials, are disclosed in the above-mentionedapplications on direct-positive emulsions, as well as in Illingsworth etal., US. Ser. No. 609,761 filed Jan. 17, 1967. An especially usefulclass of electron acceptors which can be used in the direcbpositivephotographic silver halide emulsions and processes of this invention arecyanine dyes such as the imidazo[4,5-b] quinoxaline dyes. Dyes of thisclass are described in Brooker and Van Lare, Belgian Pat. 660,253 issuedMar. 15, 1965. In these dyes, the imidazo[4,5-b] quinoxaline nucleus isattached, through the 2-carbon atom thereof, to the methine chain.

In highly preferred embodiments of this invention, good improvements inD stability are obtained when the direct-positive emulsions containelectron acceptors having the above polarog raphic halfwave potentials,and are further characterized as those which spectrally sensitize theemulsion to radiation having a wave length longer than about 480 mp. sothat the ratio of relative minus blue speed to relative blue speed ingreater than 7. Electron acceptors of this type are disclosed inIllingsworth et al., U.S. Ser. No. 609,761 filed Jan. 17, 1967.

The vacuum treatment can be achieved by any method generally used forthis purpose. In a typical embodiment, the coated element is located ina chamber and the chamber is pumped down to obtain a vacuum of at least1 torr and preferably at least 0.1 torr for at least 1 minute andpreferably at least 5 minutes. It is understood that this vacuum must beobtained at the surface of the coated element. Therefore, when rolls offilm are treated, it may take considerably longer treatment periods toachieve this vacuum at the center of the roll, depending on the width ofthe film roll, tightness of winding, etc. Generally longer pumpingperiods will be necessary with large elements or rolls of the coatedelement due to outgassing. However, improved results are generallyobtained as long as the respective portions of the element are directlysubject to the vacuum for the indicated time periods.

If desired, the vacuum chamber can be purged with inert gases, such asnitrogen, after initial pumpdown. In certain instances, it is alsodesirable to rehumidify the coated films when very lengthy vacuumperiods are used to stabilize the coated film.

After the specified pumpdown period, the coated elements can be storedin inert gases, air or the like. In certain instances, they have evenbeen stored in oxygen without the concomitant degradation in D whichusually occurs when the film is subjected to an oxygen environment.

The direct-positive emulsions of this invention also can containcompounds referred to as halogen-accepting or halogen-conductingcompounds, especially if the halide of emulsion is predominantlychloride. Useful compounds of this type are generally characterized byan anodic polarographic potential less than 0.85 and a cathodicpolarographic potential which is more negative than -1.0. Highlypreferred species of compounds of this type are merocyanine dyes havingthe above halfwave potentials. Typical compounds of this type, alongwith methods of determining the polarographic potential, are disclosedin the above-mentioned applications on direct-positive emulsions as wellas in Wise, U.S. Ser. No. 615,360 filed Feb. 13, 1967, now Patent No.3,537,858.

The emulsions of this invention can also contain the hardeners, coatingaids, surfactants, development modifiers, sensitizers, stabilizers,incorporated developer agents, binder vehicles and lubricants asdisclosed in the art for direct-positive emulsions.

The invention can be further illustrated by the following examples ofpreferred embodiments thereof.

5 EXAMPLE 1 to standard film boxes and held for 6 hours before beingexposed and processed as a group. Exposure is for 1 sec. to a 500 w.3000" K. light source in an Eastman 1B sensitometer and development isfor 6 minutes in an Elonhydroquinone developer with subsequent fixings,washing and drying. On comparing these coatings to a set of coatingswhich have been exposed and processed in the same manner soon aftercoating, there is found to be substantially no change in D on incubationat 70-50% RH.

The efiects of the 7-day incubation conditions on the D of the coatingsare shown in Table 1. The numbers in this table are the obtained maximumdensity values.

Sample 3 is like Sample 1 with a phenyl-imidazoquinoxaline-indolocarbocyanine dye (Dye I) of the type described in Brooker and Van Lare,U.S. Ser. No. 609,791, new Pat. No. 3,431,111, added to the emulsion at650 mg./-Ag mole;

Sample 4 is like Sample 1 with the combination of formaldehyde and Dye Iadded at the concentrations above.

The incubation properties of Samples 1-4 are evaluated for 7-dayincubations under the following different incubation conditions:

70-50% RH air 70-vacuum 120-vacuum 120-dry nitrogen 120-wet nitrogen120-50% RH air 120-dry oxygen 120-wet oxygen The film incubations, withthe exception of the 70- 50% air incubations, are carried out instainless-steel cylindrical bombs approximately 14- in. long x 2% in.diameter (vlume=-0.03 cu. ft.). The samples incubated at 70-50% RH inair are stored in a standard film box. The strips of the four filmsstored in vacuum, nitrogen or oxygen are placed in the bombs as a groupand pumped down in about 25 minutes to less than torr. After beingpumped down once, the samples are twice purged with the appropriate gas,and re-evacuated to less than 5Xl0- torr. in 3 min, finally being storedin vacuum, or in nitrogen or oxygen at +10 p.s.i. gauge pressure. Thestrips stored at 120-50% RH in air are not pumped down but are sealedwithout further treatment in a stain less-steel bomb under ambient roomconditions. The dry gases are conditioned by passing them through asilica gel column. The wet gases are conditioned to an unknown relativehumidity by bubbling them through a saturated aqueous Pb(NO solutionwhich at C. imparts a 98% RH to the atmosphere above the solution atequilibrium.

At the end of the 7-day incubations, the bombs held at 120 are allowedto cool overnight to room temperature and are then opened to the air.The samples are removed D losses of the films incubated in air at120-50% are substantial relative to losses under all the otherconditions. The two films, Sample 3 and Sample 4, containing Dye -I showmajor D losses in air at 120-50% RH. The distinctive treatment of thefilms stored at 120- 50% RH in air is that they are not pumped down invacuum. The pumped-down films, even those that are stored in pure oxygenat 120, are relatively stable.

Similar improvements are observed when the electronaccepting compound,Dye I, is replaced in Samples 3 and 4 with1,1-dimethyl-2,2'-diphenyl-3,3 '-indolocarbocyanine bromide;

1, 1 dime thyl-2,2', 8-tr-iphenyl-3, 3 -indolo carbocyanine perchlorate;

2,2'-di-p-methoxyphenyll, l '-dimethyl-3,3'-indol0carbocyanine bromide;

1,1',3,3 -tetraethylimidazo- [4,5 -b] quinoxalino carbocyanine chloride;or

5,5'-dichloro-3,3'-diethyl-6,6'-dinitrothiacarbocyanine iodide.

EXAMPLE 2 To show that the stabilization seen in Table 1 is the resultof pumpdown or evacuation and not the result of a nitrogen or oxygenatmosphere, sets of the coatings used in Example 1 are incubated innitrogen and oxygen atmospheres with no evacuation. The procedure is thesame as in Example 1 with the following 7-day incubation conditions:

Evacuated Purged -50% RH air l20-vaeuum -dry nitrogen Do 120-Air D0.120-dry oxyge D0 The stabilizing effect of the evacuation on the D ofall four films incubated at 120 in' nitrogen, air or oxygen isconsistently demonstrated. The stabilizing elfect of formaldehyde isalso apparent in that both the non-dyed control (Sample 1) and the dyedfilm (Sample 3) show greater 'D losses under all conditions than theirformaldehyde-containing counterparts, Sample 2 and Sample 4,respectively.

EXAMPLE 3 The vacuum treatment can also be used with spools of film.Four rolls (100 ft. x 35 mm.) of an emulsion coating similar to Sample4, i.e., containing Dye I at 570 mg./Ag mole and formaldehyde, areplaced in a vacuum chamber and evacuated for 23 hours to a pressure ofca. X10- torr. The chamber is returned to ambient room conditions(70-50% RH), then reevacuated for 1 hour to ca. 5 l0- torr and finallyreturned to ambient room conditions. The rolls of film are placed backin a metal container and are held for 4 hours prior to being incubated.One of the four rolls is kept for an additional 24 hours at roomconditions before being incubated. These rolls and three control rolls,treated and incubated for 7 days, as listed in Table 3, are compared inthe experiment. Following the incubations, the rolls are cooled to roomtemperature, are removed from the sealed bags and are conditioned for 3hours at ambient room conditions before being exposed. Duplicate stripstaken from the outside, middle and core areas of the rolls are exposedand processed as a group. The average gain or loss in D of the samplestaken from the three areas of the rolls are listed in Table 3 with the Dof the film 'kept at 70-50% RH with no vacuum treatment (Roll 1) takenas the reference (D =2.50)

hour conditioning before incubation.

I The incubations in an oxygen atmosphere are obtaied by purging theloll-lined incubation bag containing the roll with oxygen for 6 minutesimmediately before sealing the bag.

The vacuum treatment is generally efiective in stabilizing the outside,middle and core areas of the rolls. The vacuum treatment itself of Roll2 held under room-temperature conditions has little etfect on the DIncubation in air at 120 (Roll 3) with no vacuum treatment simulatingaging conditions produces an average loss in D of 0.43, while incubationof the vacuum-treated film (Roll 4) under the same conditions producesan average loss in 'D of only 0.11. Incubations in oxygen at 120 producean average 0.60 D loss for the film with no vacuum treatment (Roll 5),while the vacuumtreated tfilm (Roll 6) has an average D loss 'of onlyabout 0.07. The vacuum-treated film which is stored 24 hours under roomconditions before 120 incubation in air (Roll 7) has an average 'D lossof 0.05.

[EXAMPLE 4 Among the many possible explanations offered for thestabilization conferred on the direct-positive films by vacuum treatmentare the degassing and dehumidification of the film by the vacuum. Anattempt to separate the degassing and dehumidification efiects onstability is made by comparing desiccated strips of Sample 3 to stripsof the same sample subjected to mild degassing vacuum for short times(which would not substantially dehumidify the film).

Desiccation is for 7-6 hours over P 0 followed by 1 weeks -50% RHincubation of the desiccated film in air and 1 week of keeping ofanother sample of desiccated film at 70-50% RH to observe the effect ofdesiccation itself on the film. The effects of low vacuum on thestability are evaluated by placing duplicate 12 in. x 35 mm. strips ofSample 3 in the stainless-steel bombs (described previously) and, with amechanical vacuum pump which produces at 10- torr vacuum, pumping on thestrips for 1, 10 and 30 minutes to a 10 torr pressure followed in eachcase by two successive cycles of release of the vacuum and l-min.re-evacuation for a total of 3, 12 and 32 minutes. The severalvacuumtreated strips are incubated separately at 120 in air for 1 weekand compared with non-evacuated control strips similarly incubated. TheAD values for these films are listed in Table 4 in which the D =l.88 ofthe roomincubated control is used as the reference D for calculating theAD values of the other incubated samples.

Desiccation itself for 7-6 hours has little elfect on film D and has nosignificant stabilizing effect on the D of the incubated samplesrelative to the incubated control which shows a D loss=0.60. The lowtvacuum (l0 torr) treatments of the film produce a definitestabilization which reduces the D loss on incubation from the 0.60 valueof the control to about 0.30 for the experiments. The fact that theseshort, low-vacuum treatments produce a significant stabilization,whereas extended desiccation over P 0 does not alter the incubationstability of the film, indicates that stabilization does not occur via amoisture removal effect.

Although the invention has been described in considerable detail withparticular reference to certain preferred embodiments thereof,variations and modifications can be effected within the spirit and scopeof the invention.

I claim:

1. A process for treating a fogged, direct-positive, silver halideelement comprising subjecting said element, which comprises at least onelayer containing a fogged, direct-positive, silver halide emulsion, to avacuum of at least 1 torr at the surface of said silver halide elementfor a time suflicient to improve D stability of said silver halideemulsion.

2. A process according to claim 1 wherein said fogged, silver halideemulsion is reduction and gold fogged.

3. A process according to claim 1 wherein said fogged, direct-positive,silver halide emulsion contains an electron-accepting compound which hasan anodic polarographic halfwave potential and a cathodic halfwavepotential which, when added together, give a positive sum.

4. A process according to claim 1 wherein said fogged, direct-positive,silver halide emulsion contains an electron-accepting compound which ischaracterized as one which spectrally sensitizes the emulsion toradiation having a wave length longer than about 480 m so that the ratioof relative minus blue speed to relative blue speed is greater than 7.

10 5. A process according to claim 1 wherein a vacuum FOREIGN PATENTS ofat least 0.1 torr is maintained for at least 5 minutes. 281 700 12/1927Great Britain 34 16 6. A process according to claim 1 wherein said ele-Great Britain ment is subjected to said vacuum shortly after coating the672156 2/1939 Germany 34 16 emulsion and before exposure. 5

NORMAN G. TOROHI 'N, Primary Examiner W. H. LOUIE, JR., AssistantExaminer .U.S. C1. X.R.

References Cited UNITED STATES PATENTS 1,861,918 6/1932 Hickman 34--16 x2,115,747 5/193-8 Rafton 34-16 34161'17 '34 1,180,255 4/1916 Cossitt eta1 34-16 x

